1. Field of the Invention
The invention relates to a circuit configuration having a radar equipment for determining a distance or a relative speed between a vehicle in which the circuit configuration is disposed and an object, in particular another vehicle, the radar equipment emitting a frequency-modulated radar signal, receiving a reflected radar signal and determining the distance or the relative speed from a comparison of the emitted radar signal with the received radar signal.
Circuit configurations having a radar equipment for determining a distance or a relative speed are used in vehicles in order to make the driver aware of dangerous situations and in order to intervene automatically in the control of functions of the vehicle, such as braking and engine or airbag initiation.
The traffic situation in towns with stop-and-go traffic makes it necessary to measure the distance to a preceding vehicle, particularly at close range, that is to say between 0 and 10meters, quickly and accurately since accurate information about the distance is necessary, particularly at that range.
In a radar equipment which emits a continuously frequency-modulated radar signal that is already known from Published International Application Patent PCT/DE94/01382, corresponding to allowed U.S. application Ser. No. 08/651,564, filed May 22, 1996, different modulation rates are used for close range and for long range. At close range between 0 and 40 meters, mirror-image frequencies are suppressed by using a high modulation rate. The long range up to 400 meters is measured using a low modulation rate.